Pixel isolation elements, devices and associated methods

ABSTRACT

Light trapping pixels, devices incorporating such pixels, and various associated methods are provided. In one aspect, for example, a light trapping pixel device can include a light sensitive pixel having a light incident surface, a backside surface opposite the light incident surface, and a peripheral sidewall disposed into at least a portion of the pixel and extending at least substantially around the pixel periphery. The pixel can also include a backside light trapping material substantially covering the backside surface and a peripheral light trapping material substantially covering the peripheral sidewall. The light contacting the backside light trapping material or the peripheral light trapping material is thus reflected back toward the pixel.

PRIORITY DATA

This application is a continuation of U.S. patent application Ser. No.16/290,740, filed Mar. 1, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/216,244, filed Jul. 21, 2016, which is acontinuation of U.S. patent application Ser. No. 14/747,875, filed Jun.23, 2015, which is a continuation of U.S. patent application Ser. No.13/841,120, filed Mar. 15, 2013, which claims the benefit of U.S.Provisional Patent Application No. 61/614,275, filed on Mar. 22, 2012,each of which are incorporated herein by reference.

BACKGROUND

Image sensors are typically formed on various forms of semiconductormaterials such as, for example, silicon. Imagers can be incorporatedinto a variety of devices, including digital cameras, camcorders,computers, cell phones, etc. Due to the ever decreasing size (footprint) of these devices, image sensors have correspondingly seen adecrease in size. Backside illuminated (BSI) image sensors haveincreased in importance due to the small size of these imagers ascompared to front side illuminated (FSI) image sensors. However, pixelsize reduction can lead to a significant sacrifice in image quality. Aspixel sizes continue to decrease, image signal to noise tends todecrease while electrical and optical cross-talk between adjacent sensorpixels tends to increase. Traditional attempts to reduce the impact ofthese effects have included adding microlenses above each image sensorin front side pixel sensors to focus the light on the active detectorregions, thereby increasing efficiency and reducing cross-talk. Backsideilluminated pixel sensors can present different design considerations.For example, significant cross-talk can be generated due to reflectionoff the often planar back surface of the device.

SUMMARY

The present disclosure provides for light trapping pixels, devicesincorporating such pixels, photovoltaic solar cells, and otheroptoelectronic devices, including various associated methods. In oneaspect, for example, a light trapping device can include at least onelight sensitive pixel having a light incident surface, a backsidesurface opposite the light incident surface, and a peripheral sidewalldisposed into at least a portion of the pixel and extending at leastsubstantially around the pixel periphery. The pixel can also include abackside light trapping material substantially covering the backsidesurface and a peripheral light trapping material substantially coveringthe peripheral sidewall. The light contacting the backside lighttrapping material or the peripheral light trapping material is thusreflected back toward the pixel. In another aspect, the presentdisclosure additionally provides an array of light trapping pixels.

A variety of light trapping materials can be utilized and arecontemplated, and any such material capable of being used to trap lightin a pixel is considered to be within the present scope. In one aspect,at least one of the backside light trapping material and the peripherallight trapping material can include a high refractive index materialsandwiched between two low refractive index materials. In anotheraspect, the backside light trapping material and the peripheral lighttrapping material includes a high refractive index material sandwichedbetween two low refractive index materials. It is contemplated that thetwo low refractive index materials have a refractive index of less thanabout 2.1. Non-limiting examples of low refractive index material caninclude nitrides, oxynitrides, gasses, at least a partial vacuum, andthe like, including appropriate combinations thereof. Other non-limitingexamples of low refractive index materials can include silicon oxide,silicon nitride, silicon dioxide, and the like. Furthermore, in anotheraspect a light trapping material can include a higher refractive indexmaterial sandwiched between two materials having a refractive index thatis at least 0.2 lower as compared to the higher refractive indexmaterial. In this case, the materials are not limited by the definitionof low vs. high refractive index outlined above, but are rather definedby the relative difference in refractive index.

Furthermore, it is contemplated that high refractive index materialshave a refractive index of greater than or equal to about 2.1.Non-limiting examples of high refractive index material can includepolycrystalline silicon, amorphous silicon, single crystal silicon,multicrystalline silicon, nanocrystalline silicon, germanium, and thelike, including appropriate combinations thereof.

In one aspect, the peripheral sidewall can extend completely around thepixel periphery. In another aspect, the peripheral sidewall can extendfrom the light incident surface towards the backside surface.

In some aspects it is also contemplated that the light incident surfacecan include a frontside light trapping material at least partiallycovering the surface thereof. In one aspect, the frontside lighttrapping material can be an antireflective layer coating. In anotheraspect, the frontside light trapping material can be a reflective layerhaving an aperture to allow entry of light into the pixel, wherein thereflective layer is operable to reflect light impinging thereupon frominside the pixel back into the pixel. In some aspects it can bebeneficial to include a lens functionally coupled to the aperture andoperable to focus incident light through the aperture and into thepixel.

In another aspect the present disclosure additionally provides asubstantially light trapping pixel device including a light sensitivepixel having a light incident surface, a backside surface opposite thelight incident surface, and a peripheral sidewall extending from thelight incident surface to the backside surface and extending around thepixel periphery. The pixel additionally includes a backside lighttrapping material substantially covering the backside surface, and aperipheral light trapping material substantially covering the peripheralsidewall. Furthermore, an internally reflective frontside light trappingmaterial can cover at least a portion of the light incident surface thatis operable to allow entrance of light into the pixel and is operable toreflect light impinging thereupon from inside the pixel back into thepixel, and the light contacting the backside light trapping material orthe peripheral light trapping material is reflected back toward thepixel.

In yet another aspect, the present disclosure provides a method ofmaking a light trapping device, including forming at least one pixel byforming a backside light trapping material on a semiconductor layer, thebackside light trapping material including a high refractive indexmaterial sandwiched between two low refractive index materials, andforming a pixel device layer on the semiconductor layer opposite thelight trapping material. The method can additionally include etching atrench circumscribing the pixel device layer and filling the trench witha light trapping material. In some aspects, the trench can be etched toa depth that contacts at least the first low refractive index material.In some aspects, an incident light trapping material can be applied tothe pixel device layer. It is also noted that the light trappingmaterial can be located anywhere in the backside region of the device,and that the current scope is not limited to the location of materialsor the manufacturing method described above.

In another aspect, filling the trench with the light trapping materialcan further include depositing a low refractive index material into thetrench to fill a portion of the trench from the trench walls inward,ceasing deposition of the low refractive index material to leave aninternal space within the trench, and depositing a high refractive indexmaterial into the trench to fill the internal space.

In another aspect, the method can include forming a textured region onat least a portion of the semiconductor layer between the semiconductorlayer and the first low refractive index prior to depositing the firstlow refractive index material onto the semiconductor layer. Non-limitingexamples of techniques for forming the textured region include plasmaetching, reactive ion etching, porous silicon etching, lasing, chemicaletching, nanoimprinting, material deposition, selective epitaxialgrowth, the like, including appropriate combinations thereof. In onespecific aspect, forming the textured region includes laser texturing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and advantage of the presentdisclosure, reference is being made to the following detaileddescription of embodiments and in connection with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view of multiple image sensor pixels inaccordance with an embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of multiple image sensor pixels inaccordance with another embodiment of the present disclosure;

FIG. 3 is a cross-sectional view of multiple image sensor pixels inaccordance with another embodiment of the present disclosure;

FIG. 4 is a cross-sectional view of a light trapping pixel in accordancewith another embodiment of the present disclosure;

FIG. 5 is a cross-sectional view of a light trapping pixel in accordancewith another embodiment of the present disclosure;

FIG. 6 is a cross-sectional view of a light trapping pixel in accordancewith another embodiment of the present disclosure; and

FIG. 7 is a depiction of a method of making a light trapping pixel inaccordance with yet another aspect of the present disclosure.

DETAILED DESCRIPTION

Before the present disclosure is described herein, it is to beunderstood that this disclosure is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

Definitions

The following terminology will be used in accordance with thedefinitions set forth below.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” and, “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a dopant” includes one or more of such dopants andreference to “the layer” includes reference to one or more of suchlayers.

As used herein, the terms “light” and “electromagnetic radiation” can beused interchangeably and can refer to electromagnetic radiation in theultraviolet, visible, near infrared and infrared spectra. The terms canfurther more broadly include electromagnetic radiation such as radiowaves, microwaves, x-rays, and gamma rays. Thus, the term “light” is notlimited to electromagnetic radiation in the visible spectrum. Manyexamples of light described herein refer specifically to electromagneticradiation in the visible and infrared (and/or near infrared) spectra.For purposes of this disclosure, visible range wavelengths areconsidered to be from approximately 350 nm to 800 nm and non-visiblewavelengths are considered to be longer than about 800 nm or shorterthan about 350 nm. Furthermore, the infrared spectrum is considered toinclude a near infrared portion of the spectrum including wavelengths ofapproximately 800 to 1100 nm, a short wave infrared portion of thespectrum including wavelengths of approximately 1100 nm to 3micrometers, and a mid-to-long wavelength infrared (or thermal infrared)portion of the spectrum including wavelengths greater than about 3micrometers up to about 30 micrometers. These are generally andcollectively referred to herein as “infrared” portions of theelectromagnetic spectrum unless otherwise noted.

As used herein, “quantum efficiency” (QE) is typically referring to“external quantum efficiency” (EQE) which is defined as the ratio ofelectrons collected per photons incident on an optoelectronic device.“Internal quantum efficiency” is defined as the ratio of electronscollected per photons absorbed by an optoelectronic device.

As used herein, the terms “3D” and “three dimensional” can be usedinterchangeably, and refer to obtaining distance information usingelectromagnetic radiation.

As used herein, the terms “disordered surface” and “textured surface”can be used interchangeably, and refer to a surface having a topologywith nano- to micron-sized surface variations. Such a surface topologycan be formed by the irradiation of a laser pulse or laser pulses,chemical etching, wet or dry etching including masked or masklessetching, lithographic patterning, interference of multiple simultaneouslaser pulses, reactive ion etching, plasma etching or any othertechnique that can be used to form such a topology. While thecharacteristics of such a surface can be variable depending on thematerials and techniques employed, in one aspect such a surface can beseveral hundred nanometers thick and made up of nanocrystallites (e.g.from about 10 to about 50 nanometers), nanopores, and the like. Inanother aspect, such a surface can include micron-sized structures (e.g.about 1 μm to about 60 μm). In yet another aspect, the surface caninclude nano-sized and/or micron-sized structures from about 5 nm andabout 500 μm. A variety of criteria can be utilized to measure the sizeof such structures. For example, for cone-like structures the aboveranges are intended to be measured from the peak of a structure to thevalley formed between that structure and an adjacent neighboringstructure. For structures such as nanopores, the above ranges areintended to be approximate diameters. Additionally, the surfacestructures can be spaced at various average distances from one another.In one aspect, neighboring structures can be spaced at a distance offrom about 50 nm to about 50 μm. In another aspect, neighboringstructures can be spaced at a distance of from about 50 nm to about 2μm. Such spacing is intended to be from a center point of one structureto the center point of a neighboring structure.

As used herein, the term “fluence” refers to the amount of energy from asingle pulse of laser radiation that passes through a unit area. Inother words, “fluence” can be described as the energy density of onelaser pulse.

As used herein, the term “target region” refers to an area of asemiconductor material that is intended to be doped or surface modified.The target region of a semiconductor material can vary as the surfacemodifying process progresses. For example, after a first target regionis doped or surface modified, a second target region may be selected onthe same semiconductor material.

As used herein, the term “absorptance” refers to the fraction ofincident electromagnetic radiation absorbed by a material or device.

As used herein, the term “monolithic” refers to an electronic device inwhich electronic components are formed on the same substrate. Forexample, two monolithic pixel elements are pixel elements that areformed on the same semiconductor substrate.

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result. For example, a composition that is“substantially free of” particles would either completely lackparticles, or so nearly completely lack particles that the effect wouldbe the same as if it completely lacked particles. In other words, acomposition that is “substantially free of” an ingredient or element maystill actually contain such item as long as there is no measurableeffect thereof.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc., as well as 1, 2, 3, 4, and 5, individually.

This same principle applies to ranges reciting only one numerical valueas a minimum or a maximum. Furthermore, such an interpretation shouldapply regardless of the breadth of the range or the characteristicsbeing described.

THE DISCLOSURE

The present disclosure provides semiconductor devices and associatedmethods that can exhibit various enhanced properties, such as, forexample, enhanced light detection properties. More specifically, in oneaspect the disclosure relates to image sensor pixels and elements fortrapping light within such pixels. In other aspects, various lighttrapping elements can additionally isolate neighboring pixels in animage sensor. Isolation elements can be configured to optically and/orelectrically isolate neighboring pixels from one another in addition totrapping light with in the pixel. It is additionally contemplated thatthe present disclosure is applicable to other optoelectronic devicessuch as solar cells, and that all such should be included in the presentscope.

In various aspects, image sensors can be front side or backsideilluminated, 3D sensors, or any other device or system that incorporatea unique isolation element configured to reduce cross-talk between pixelelements. For example, in one aspect an image sensor can be capable ofdetecting visible and infrared light, whereas an isolation elementassociated with such an imager can be designed and configured to reduceand in some cases eliminate electrical and/or optical cross-talk betweenneighboring pixels from straying visible and infrared light. In somecases, isolation elements can be doped with a dopant that enables therepelling of electrical carriers from the isolation elements or in otherwords from the side walls of the device. In other cases, isolationelements can include light trapping or reflective materials to opticallyisolate neighboring pixels. It is additionally contemplated thatisolation elements can include both a dopant and a light trapping orreflective material to both electrically and optically isolate thepixels. Moreover, isolation elements can also include surface featuresformed thereon or associated therewith. Additionally, in some cases apixel can include a textured region to enhance the detection of infraredlight among other things.

In one aspect, a variety of optoelectronic devices are provided such as,without limitation, photosensitive diodes, pixels, and imagers capableof detecting visible and infrared light while exhibiting reduced opticaland electrical cross-talk between neighboring pixels or diodes. It isalso contemplated that the present scope include methods associated withsuch devices, including methods of making and using. The present devicescan additionally exhibit enhanced absorption and quantum efficiencies.Such devices can also include a plurality of photodiodes or pixels. Insome cases, the present devices can achieve a quantum efficiency of 10%for wavelengths at 1064 nm and having a thickness of less than 10microns. In another embodiment, the present device can achieve a quantumefficiency of about 20% for wavelengths at 940 nm and a thickness ofless than 10 microns.

In one aspect, a device can include at least a semiconductor substratehaving a first side for receiving incident light and a second sideopposite the first side. Either or both the first or second sides caninclude at least one doped region. Furthermore, the image sensor caninclude at least one isolation element or feature for at least partiallyseparating and isolating neighboring pixels. FIG. 1 illustrates asimplified drawing of an imager having a first pixel 102 and a secondpixel 104, that are formed monolithically on a common semiconductorsubstrate 106 and are isolated from one another by an isolation element114. Doped regions 108 and 110 can be disposed on either the first side120 or second side 122 of the semiconductor substrate, or in some caseson opposite sides of the device. In the present figure, the device isconfigured such that the first side is capable of receiving incidentlight. A textured region 112 having surface features is shown on thesecond side 122 of the semiconductor substrate 106. This architecturehaving the texture region 112 on the back side 122 can enable enhanceddetection and absorption of electromagnetic radiation having wavelengthsin the range of about 600 nm to about 1200 nm. It should be noted thatthis architecture can be used in either a FSI or BSI image sensorarchitecture. Furthermore, the textured region can be located on thefirst side 120, the second side 122, or both the first and second sides.

In a typical FSI imager, incident light enters the semiconductor deviceby first passing by transistors and metal circuitry. The light, however,scatters off of the transistors and circuitry prior to entering thelight sensing portion of the imager, thus causing optical loss andnoise. A lens can be disposed on the topside of a FSI pixel to directand focus the incident light to the light sensing active region of thedevice, thus partially avoiding the circuitry. BSI imagers, one theother hand, are configured to have the light sensing portion of thedevice opposite the circuitry. Incident light enters the device via thelight sensing portion and is at least partially absorbed by the deviceprior to reaching the circuitry. BSI designs allow for smaller pixelarchitecture and a high fill factor for the imager. As mentioned, thedevices according to aspects of the present disclosure can be adaptedfor either configuration. It should also be understood that devicesaccording to aspects of the present disclosure can be incorporated intocomplimentary metal-oxide-semiconductor (CMOS) imager architectures orcharge-coupled device (CCD) imager architectures, as well as otheroptoelectronic devices.

Regarding isolation elements, also referred to herein as trenchisolation features or sidewalls, various processes can be employed toform the isolation elements. It is contemplated that the isolationfeatures can extend from either the first surface or the second surfaceinto the semiconductor material and depending on the depth of the trenchcan be considered either deep trench isolation or shallow trenchisolation. The dimensions of the trench can vary, depending on theapplication. For example, trenches can have parallel walls, or they canhave sloping walls, bottle neck architecture, or any other usefulconfiguration. The depth of the trench isolation feature can be in therange of from about 100 nm to about 50 μm depending on the design of thedevice. The width can be in the range of from about 100 nm to about 10μm. For simplicity, the figures in this disclosure show deep trenchisolation but it should be understood that shallow trench isolationarchitectures can be utilized, and that deep trench isolation need notcompletely extend from one side to the other. The processes contemplatedfor forming trenches or other isolation features can include, reactiveion etch, isotropic plasma etch, wet chemical etch, laser irradiation,or any other known etch technique.

A variety of reflective materials can be utilized in constructing theisolation features in order to provide optical isolation, lighttrapping, and/or electrical isolation, and any such material capable ofincorporation into a photosensitive device is considered to be withinthe present scope. Non-limiting examples of such materials include aBragg reflector, a metal reflector, a metal reflector over a dielectricmaterial, a transparent conductive oxide such as zinc oxide, indiumoxide, or tin oxide, and the like, including combinations thereof.Non-limiting examples of metal reflector materials can include silver,aluminum, gold, platinum, reflective metal nitrides, reflective metaloxides, and the like, including combinations thereof. In one specificaspect, the dielectric layer can include an oxide layer and thereflecting region can include a metal layer. The surface of the metallayer on an oxide acts as a mirror-like reflector for the incidentelectromagnetic radiation. In addition, in some aspects trench isolationfeatures can be doped to further affect the properties of the materialwith respect to electrical isolation.

In one specific aspect, a reflective region can include a transparentconductive oxide, an oxide, and a metal layer. The transparent oxide canbe textured and a metal reflector deposited thereupon. The texturedsurface of the metal on a roughened transparent conductive oxide can actas a diffusive scattering site for the incident electromagneticradiation.

In some cases, materials having disparate properties can be utilized inthe trench isolation features in order to derive a useful combinedinteraction. As is shown in FIG. 2, for example, an imager having atleast two pixels or photodiodes (202 and 204) and at least one isolationelement 214. The pixels are shown formed monolithically on a commonsemiconductor substrate 206. Doped regions 208 and 210 can be disposedon either the first side 220 or second side 222 of the semiconductorsubstrate. A textured region 212 having surface features is created onthe second side 222 of the semiconductor substrate 206.

In some aspects, the isolation element 214 can be designed to functionas a Bragg reflector. In such cases, the isolation element 214 includesat least two layers 216 comprised of material having a lower refractiveindex (n) as compared to the material of the third layer 218 disposed orsandwiched therebetween. In other words, the isolation element includesa high refractive index material sandwiched between two low refractiveindex materials, and such a configuration forms a Bragg reflector.Additionally, in some aspects the low reflective index materials can bechosen to have a lower refractive index as compared to the semiconductorsubstrate 206.

Furthermore, in another aspect an isolation element or light trappingmaterial can include a higher refractive index material sandwichedbetween two materials having a refractive index that is at least 0.2lower as compared to the higher refractive index material. In this case,the materials are not limited by the definition of low vs. highrefractive index outlined below, but are rather defined by the relativedifference in refractive index. For example, in one aspect a lighttrapping material can include silicon dioxide/silicon nitride/silicondioxide, each material of which would be considered to be a lowrefractive index material. There is, however, a greater than 0.2difference in the refractive indexes between silicon dioxide and siliconnitride, and thus such an isolation element would be included within thepresent scope. It is also noted that the light trapping material canhave greater than three layers. As one non-limiting example, a materialcan have silicon dioxide/silicon nitride/polysilicon/siliconnitride/silicon dioxide.

As has been described, in some aspects a Bragg reflector can be utilizedas an isolation element to trap electromagnetic radiation within thepixel. A Bragg reflector is a structure formed from multiple layers ofalternating materials with varying refractive indexes, or by a periodicvariation of some characteristic (e.g. height) of a dielectricwaveguide, resulting in periodic variation in the effective refractiveindex in the guide. Each layer boundary causes a partial reflection ofan optical wave. For waves whose wavelength is close to four times theoptical thickness of the layers, the many reflections combine withconstructive interference, and the layers act as a high-qualityreflector. Thus the coherent super-positioning of reflected andtransmitted light from multiple interfaces in the structure interfere soas to provide the desired reflective, transmissive, and absorptivebehavior. In one aspect, a Bragg reflector can be made as in FIG. 2,whereby a high refractive index material sandwiched between two lowrefractive index materials. In one specific aspect, for example, theBragg reflector can be constructed of a layer of polysilicon sandwichedbetween two layers of silicon dioxide. Because of the high refractiveindex difference between silicon and silicon dioxide, and the thicknessof these layers, this structure can be fairly low loss even in regionswhere bulk silicon absorbs appreciably. Additionally, because of thelarge refractive index difference, the optical thickness of the entirelayer set can be thinner, resulting in a broader-band behavior and fewerfabrications steps.

In terms of optical isolation from pixel to pixel, the large index ofrefraction mismatch can result in total reflection at the trench sidewalls. To prevent excessive dark current in the pixels, a passivationlayer may be disposed on the side walls of the trench to prevent thegeneration of carriers and leakage current. Silicon nitride depositedover a thin grown oxide layer is also commonly used, in this case theoxide may be a low temperature grown plasma oxide.

It can be shown through calculations that a low recombination velocityof silicon oxide and silicon nitride is the result of moderately highpositive oxide charge (5×10¹¹ to 1×10¹² cm⁻²) and relatively low midgapinterface state density (1×10¹⁰ to 4×10¹⁰ cm⁻² eV⁻¹). The addition ofsilicon oxide or nitride can reduce surface recombination and surfacegeneration. Reducing the surface recombination can increase quantumefficiency of photon collection and surface generation can causeexcessive dark current in the imagers thereby reducing the quality ofthe image.

Since the positive oxide charge of silicon nitride or silicon oxynitrideis relatively low on silicon on insulator imagers a p-type layer can beadjacent the silicon oxide, silicon oxynitride and/or silicon nitridelayers as an alternative embodiment. In this case the p-type layer willaccumulate the surface or the backside of the p-type silicon layer andp-type sidewalls.

Other possible passivation techniques include a hot steam anneal ofhydrogenated silicon nitride or the use of amorphous silicon.

Aluminum oxide can also be deposited in the trench to form an isolatingbarrier. Aluminum oxide can have low stress, a negative fixed charge andhigher index of refraction than silicon oxide or low stress siliconoxynitride nitride. Low surface recombination velocities, as low as 10cm/s can be obtained through various deposition processes of Al₂O₃layers on the silicon substrate. Low surface recombination can beachieved by field induced surface passivation due to a high density ofnegative charges stored at the interface. PECVD aluminum oxide isdescribed here for the backside passivation of the backside and backsidetrenches in backside illuminated image sensors.

The index of refraction of the aluminum oxide can be increased slightlyas required by the addition of other metallic elements to make ternaryinsulators like Aluminum Oxynitride (AlON), Hafnium Aluminum Oxide(HfAlO), Zirconium Aluminum Oxide (ZrAlO), Lanthanum Aluminum Oxide(LaAlO), Titanium Aluminum Oxide (TiAlO) or quaternary dielectrics likeHafnium Aluminum Oxynitride (HfAlON), Tantalum Aluminum Oxynitride(TaAlON), Lanthanum Aluminum Oxynitride (LaAlON).

Low temperature PECVD deposition processes are contemplated for thebackside passivation of the backside and backside trenches in backsideilluminated image sensors. As previously mentioned the large index ofrefraction mismatch between silicon and the insulators in the trenchesresults in reflection of the incident light and provides opticalisolation. The trenches also provide electrical isolation. Additionally,it can also be beneficial to dope the sidewalls to create a surfacefield that will improve electrical isolation between the pixels. In oneaspect, it can also be beneficial to dope the low refractive indexmaterial of the Bragg-type reflectors to increase such electricalisolation.

Returning to FIG. 2, layers the silicon oxide and polysilicon canoptically and electrically isolate the adjacent pixels, as well asfunction to trap light within the pixel. While any thicknesses capableof forming such a reflector are considered to be within the presentscope, layer 216 can have a thickness in the range of from about 50 nmto about 500 nm. Layer 118 can have a thickness in the range of fromabout 5 nm to about 100 nm. Thus, the difference in refractive indexesand thickness can determine the intensity of the internal reflection ofelectromagnetic radiation. Notably, other materials such as metals, aswell as other material not listed herein can be used to increaseinternal reflection of the light.

It is noted that, for the purposes of the present disclosure, in oneaspect a low refractive index material can have a refractive index ofless than about 2.1. In the case of the sandwiched materials, the twolow refractive index materials can be the same or different materialshaving a refractive index of less than about 2.1. Non-limiting examplesof low refractive index materials can include oxides, nitrides,oxynitrides, gasses, at least a partial vacuums, and the like, includingappropriate combinations thereof. Non-limiting specific examples of suchmaterials can include silicon oxide, silicon nitride, siliconoxynitride, and the like, including combinations thereof. Additionally,a high K dielectric material can also make a suitable low reflectiveindex material due to their low refractive index properties and gooddielectric properties, and as such, are considered to be within thepresent scope. One example is Hafnium oxide, which has a refractiveindex of about 1.9. Other examples of high K dielectrics include hafniumsilicate, zirconium silicate, zirconium dioxide, and the like.

Additionally, in another aspect a high refractive index material caninclude a material having a refractive index of greater than or equal toabout 2.1. Thus, in the case of the sandwiched materials, the highrefractive index material disposed between the low refractive indexmaterials has a refractive index of about 2.1 or greater. Non-limitingexamples of high refractive index materials can include polycrystallinesilicon, amorphous silicon, single crystal silicon, multicrystallinesilicon, nanocrystalline silicon, germanium, and the like, includingappropriate combinations thereof.

In still another aspect of the present disclosure, a photosensitiveimager having at least two pixels (302 and 304) and at least one trenchisolation region 314 is shown in FIG. 3. The pixels can include asemiconductor substrate 306, having a first and second surface, 320 and322 respectively; at least two doped regions 308 and 310, and a texturedregion 312 formed at least on the opposite side of the light incidentsurface (i.e. the second side 322). The textured region 312 can havesurface features configured to reflect and disperse light. Further, thesidewalls can include a texture region 312 to increase the internalreflections of light. Regarding the isolation element 314 in FIG. 3, theisolation element can include several layers of materials that canpassivate the sidewalls and each have a different index of refraction,as was described in FIG. 2. Further, a textured region 312 can be formedon the side walls of the isolation element(s) 314.

The present disclosure additionally provides pixels and imager devices,including imager arrays, which trap light therewithin. In one aspect asis shown in FIG. 4, for example, a light trapping pixel device caninclude a light sensitive pixel or device 402 having a light incidentsurface 420, a backside surface 422 opposite the light incident surface420, and a peripheral sidewall 424 disposed into at least a portion ofthe pixel 402 and extending at least substantially around the pixelperiphery. It is noted that the pixel sidewall is also known as atrench. The pixel can also include a backside light trapping material426 substantially covering, partially covering, or completely coveringthe backside surface 422. A peripheral light trapping material 428 canbe substantially covering, partially covering, or completely coveringthe peripheral sidewall 424. As such, light contacting the backsidelight trapping material 426 or the peripheral light trapping material428 is reflected back toward the pixel 402. Also shown in FIG. 4 are atleast two doped regions 408 and 410 and an optional textured region 412.It is noted that, in addition to a single pixel as shown, pixel arraysare also contemplated and are to be included in the present scope.

The light trapping materials of FIG. 4 can be as described above, eithersingle or multiple layer structures. In one aspect, for example, atleast one of the backside light trapping material 426 and the peripherallight trapping material 428 includes a high refractive index materialsandwiched between two low refractive index materials. In anotheraspect, the backside light trapping material 426 and the peripherallight trapping material 428 includes a high refractive index materialsandwiched between two low refractive index materials. It is noted thatthese light trapping materials are shown in FIG. 4 as a single layer forclarity, and that multiple layers are contemplated. Furthermore, theperipheral sidewall can extend for a portion, a substantial portion, orcompletely around the pixel periphery. Additionally, as has beendescribed herein, the peripheral sidewall can extend partially into thepixel, substantially through the pixel, or completely through the pixelto the backside surface. Thus, both deep and shallow trenches arecontemplated.

In another aspect, as is shown in FIG. 5, a pixel 502 can include afrontside light trapping material 530 that at least partially covers,substantially covers, or completely covers the light incident surface520. The frontside light trapping material 530 can be multiple layer ofmaterials have a variety of properties and uses, including passivation,antireflection, light trapping, and the like, including combinationsthereof. Note that numerical indicators in FIG. 5 from previous figuresare intended to reflect the previous descriptions for those elements,and as such, reference is made to FIG. 4.

In another aspect, as is shown in FIG. 6, a pixel 602 can include afrontside light trapping material 632 associated with the light incidentsurface 620 that is an internal reflective layer having an aperture 634to allow entry of light 690 into the pixel 602. The frontside lighttrapping material 632 is thus operable to reflect light impingingthereupon from inside the pixel 602 back into the pixel. Additionally,in some aspects a lens 636 can be functionally coupled to the aperture634 to focus incident light 690 through the aperture 634 and into thepixel 602. The effective surface area of the aperture compared to thefrontside surface area of the pixel can vary depending on the design ofthe device and the presence, absence, or particular properties of alens. In one aspect, however, the aperture can be large enough to acceptand trap incoming light to a degree that increases the efficiency of thepixel. In one specific aspect, the aperture has an effective surfacearea of less than about 90% of the incident light surface total surfacearea. It is noted that various elements such as the doped regions andthe optional textured layer are not shown in FIG. 6 for clarity.Furthermore, numerical indicators in FIG. 6 from previous figures areintended to reflect the previous descriptions for those elements, and assuch, reference is made to FIG. 4.

The frontside light trapping material can be made of a variety ofmaterials including metals as have been described herein with respect toother light trapping materials. As such, any material that can beapplied to the light incident surface and that is internally reflectivetoward the inside of the pixel is considered to be within the presentscope. Thus, the aforementioned pixel is reflective on 6 internal sides,and as such, light entering the pixel that is not absorbed will interactwith and be reflected internally be either the backside, peripheralsidewall, or frontside light trapping materials. Light is thuseffectively maintained inside the pixel until it is absorbed.

In another aspect of the present disclosure, a method of making a lighttrapping pixel device is provided. Such a method can include, as isshown in FIG. 7, 702 forming a pixel by: 704 forming a backside lighttrapping material on a semiconductor layer, the backside light trappingmaterial including a high refractive index material sandwiched betweentwo low refractive index materials, and 706 forming a pixel device layeron the semiconductor layer opposite the light trapping material. Themethod can additionally include 708 etching a trench circumscribing thepixel device layer and 710 filling the trench with a light trappingmaterial. Further details regarding the wafer bonding and wafer-bondedstructures described can be found in copending U.S. application Ser. No.13/069,135, filed on Mar. 22, 2011, which is incorporated herein byreference.

The formation of the backside light trapping material can beaccomplished by a variety of techniques, all of which are considered tobe within the present scope. In one aspect, for example, depositing afirst low refractive index material onto the semiconductor layer,bonding the first low refractive index material to a high refractiveindex material having a second low refractive index material coupledthereto such that the high refractive index material is sandwiched inbetween the first and second low refractive index materials. In somecases the second low refractive index material can be coupled to acarrier wafer. In another aspect, the first low refractive index can bedeposited onto the semiconductor layer followed by deposition of thehigh refractive index material and then the second low refractive indexmaterial. In another aspect, the layered structure can be formed on acarrier wafer, and the outermost low refractive index material can thenbe bonded to the semiconductor layer. The carrier wafer can then beoptionally removed. In yet another aspect, the first refractive indexmaterial can be deposited onto the semiconductor layer, the secondrefractive index material can be deposited onto a carrier wafer, and thehigh refractive index material can be deposited onto either the first orsecond refractive index material, followed by bonding of the structuretogether.

As has been described, the trench can be a shallow trench or a deeptrench. In one aspect, however, etching the trench circumscribing thepixel device layer can further include etching the trench to a depththat contacts at least the first low refractive index material.Furthermore, the method can also include applying an incident lighttrapping material to the pixel device layer.

In some aspects the various trenches can be filled with a material, orthey can be gas filled or have a partial vacuum applied thereto. Forthose aspects whereby the trenches will be filled in with a non-gasmaterial, a variety of deposition techniques are contemplated and allare considered to be within the present scope. In one aspect, however,the trench can be filled with a high refractive index material and a lowrefractive index material in a sandwich structure as has been described.In one exemplary technique, the filling of the trench with such lighttrapping material can include depositing a low refractive index materialinto the trench to fill a portion of the trench from the trench wallsinward, ceasing deposition of the low refractive index material to leavean internal space within the trench, and depositing a high refractiveindex material into the trench to fill the internal space. As such, thesandwiched layer of low-high-low refractive index materials is thuscreated in the trench.

In another aspect, the method can also include forming a textured regionon at least a portion of the semiconductor layer between thesemiconductor layer and the first low refractive index prior todepositing the first low refractive index material onto thesemiconductor layer. Non-limiting examples of texture formationtechniques can include plasma etching, reactive ion etching, poroussilicon etching, lasing, chemical etching, nanoimprinting, materialdeposition, selective epitaxial growth, and combinations thereof. In onespecific aspect, the textured region includes laser texturing.

A device design having a textured region located on, for example, theback surface of a photodetector, provides significant performancebenefits. The textured region can have surface features that can lead tohigher recombination of photocarriers for short wavelengths (e.g. in theblue green part of the spectrum) due to the very shallow penetration ofthose wavelengths into the detecting volume of the device. By physicallylocating the textured on the back surface of the device, a pristinesurface is provided for the collection of short wavelengths on the topsurface (i.e. the light incident surface), and the longer wavelengthsthat penetrate deep into or through the detecting region of thesemiconductor material are collected by or with the help of the texturedregion opposite the light incident surface.

The textured region can be of various thicknesses, depending on thedesired use of the material. In one aspect, for example, the texturedregion has a thickness of from about 500 nm to about 100 μm. In anotheraspect, the textured region has a thickness of from about 500 nm toabout 15 μm. In yet another aspect, the textured region has a thicknessof from about 500 nm to about 2 μm. In a further aspect, the texturedregion has a thickness of from about 500 nm to about 1 μm. In anotheraspect, the textured region has a thickness of from about 200 nm toabout 2 μm.

The textured region can function to diffuse electromagnetic radiation,to redirect electromagnetic radiation, and/or to absorb electromagneticradiation, thus increasing the quantum efficiency of the device. Thetextured region can include surface features to further increase theeffective absorption length of the device. Non-limiting examples ofshapes and configurations of surface features include cones, pillars,pyramids, micolenses, quantum dots, inverted features, gratings,protrusions, sphere-like structures, and the like, includingcombinations thereof. Additionally, surface features can bemicron-sized, nano-sized, or a combination thereof. For example, cones,pyramids, protrusions, and the like can have an average height withinthis range. In one aspect, the average height would be from the base ofthe feature to the distal tip of the feature. In another aspect, theaverage height would be from the surface plane upon which the featurewas created to the distal tips of the feature. In one specific aspect, afeature (e.g. a cone) can have a height of from about 50 nm to about 2μm. As another example, quantum dots, microlenses, and the like can havean average diameter within the micron-sized and/or nano-sized range.

In addition to or instead of surface features, the textured region caninclude a textured film layer. In one aspect, for example, the texturedregion can include a substantially conformal textured film layer. Such atextured film layer can have an average thickness of from about 1 nm toabout 20 μm. In those aspects where the textured region includes surfacefeatures, the conformal textured film layer can have a varying thicknessrelative to the location on the surface features upon which isdeposited. In the case of cones, for example, the conformal texturedfilm layer can become thinner toward the tips of the cones. Such aconformal film layer can include various materials, including, withoutlimitation, SiO₂, Si₃N₄, amorphous silicon, polysilicon, a metal ormetals, and the like, including combinations thereof. The conformaltextured film layer can also be one or more layers of the same ordifferent materials, and can be formed during the creation of surfacefeatures or in a separate process.

Textured regions according to aspects of the present disclosure canallow a photosensitive device to experience multiple passes of incidentelectromagnetic radiation within the device, particularly at longerwavelengths (i.e. infrared). Such internal reflection increases theeffective absorption length to be greater than the thickness of thesemiconductor layer. This increase in absorption length increases thequantum efficiency of the device, leading to an improved signal to noiseratio.

The texturing process can texture the entire substrate to be processedor only a portion of the substrate. In one aspect, for example, asubstrate such as the semiconductor layer can be textured and patternedby an appropriate technique over an entire surface to form the textureregion. In another aspect, a substrate such as the semiconductor layercan be textured and patterned across only a portion of a surface byusing a selective etching technique, such as a mask, photolithography,and an etch or a laser process to define a specific structure orpattern.

In addition to surface features, the textured region can have a surfacemorphology that is designed to focus or otherwise direct electromagneticradiation. For example, in one aspect the textured region has a surfacemorphology operable to direct electromagnetic radiation into thesemiconductor layer. Non-limiting examples of various surfacemorphologies include sloping, pyramidal, inverted pyramidal, spherical,square, rectangular, parabolic, asymmetric, symmetric, and the like,including combinations thereof.

The textured region, including surface features as well as surfacemorphologies, can be formed by various techniques, including plasmaetching, reactive ion etching, porous silicon etching, lasing, chemicaletching (e.g. anisotropic etching, isotropic etching), nanoimprinting,material deposition, selective epitaxial growth, and the like.

One effective method of producing a textured region is through laserprocessing. Such laser processing allows discrete target areas of asubstrate to be textured, as well as entire surfaces. A variety oftechniques of laser processing to form a textured region arecontemplated, and any technique capable of forming such a region shouldbe considered to be within the present scope. Laser treatment orprocessing can allow, among other things, enhanced absorption propertiesand thus increased electromagnetic radiation focusing and detection.

In one aspect, for example, a target region of the substrate to betextured can be irradiated with laser radiation to form a texturedregion. Examples of such processing have been described in furtherdetail in U.S. Pat. Nos. 7,057,256, 7,354,792 and 7,442,629, which areincorporated herein by reference in their entireties. Briefly, a surfaceof a substrate material is irradiated with laser radiation to form atextured or surface modified region. Such laser processing can occurwith or without a dopant material. In those aspects whereby a dopant isused, the laser can passed through a dopant carrier and onto thesubstrate surface. In this way, dopant from the dopant carrier isintroduced into the target region of the substrate material. Such aregion incorporated into a substrate material can have various benefitsin accordance with aspects of the present disclosure. For example, thetextured region typically has a textured surface that increases thesurface area and increases the probability of radiation absorption. Inone aspect, such a textured region is a substantially textured surfaceincluding micron-sized and/or nano-sized surface features that have beengenerated by the laser texturing. In another aspect, irradiating thesurface of a substrate material includes exposing the laser radiation toa dopant such that irradiation incorporates the dopant into thesubstrate. Various dopant materials are known in the art, and arediscussed in more detail herein.

Thus the surface of the substrate at the target region is thuschemically and/or structurally altered by the laser treatment, whichmay, in some aspects, result in the formation of surface featuresappearing as structures or patterned areas on the surface and, if adopant is used, the incorporation of such dopants into the substratematerial. In some aspects, the features or structures can be on theorder of 50 nm to 20 μm in size and can assist in the absorption ofelectromagnetic radiation. In other words, the textured surface canincrease the probability of incident radiation being absorbed.

A variety of semiconductor materials are contemplated for use with thepixel devices and methods according to aspects of the presentdisclosure. Such materials can be utilized as the semiconductor layerand/or the semiconductor substrate, as well as for the secondarysemiconductor layer and the epitaxially grown semiconductor layer.Non-limiting examples of such semiconductor materials can include groupIV materials, compounds and alloys comprised of materials from groups IIand VI, compounds and alloys comprised of materials from groups III andV, and combinations thereof. More specifically, exemplary group IVmaterials can include silicon, carbon (e.g. diamond), germanium, andcombinations thereof. Various exemplary combinations of group IVmaterials can include silicon carbide (SiC) and silicon germanium(SiGe). In one specific aspect, the semiconductor material can be orinclude silicon. Exemplary silicon materials can include amorphoussilicon (a-Si), microcrystalline silicon, multicrystalline silicon, andmonocrystalline silicon, as well as other crystal types. In anotheraspect, the semiconductor material can include at least one of silicon,carbon, germanium, aluminum nitride, gallium nitride, indium galliumarsenide, aluminum gallium arsenide, and combinations thereof.

Exemplary combinations of group II-VI materials can include cadmiumselenide (CdSe), cadmium sulfide (CdS), cadmium telluride (CdTe), zincoxide (ZnO), zinc selenide (ZnSe), zinc sulfide (ZnS), zinc telluride(ZnTe), cadmium zinc telluride (CdZnTe, CZT), mercury cadmium telluride(HgCdTe), mercury zinc telluride (HgZnTe), mercury zinc selenide(HgZnSe), and combinations thereof.

Exemplary combinations of group III-V materials can include aluminumantimonide (AlSb), aluminum arsenide (AlAs), aluminum nitride (AlN),aluminum phosphide (AlP), boron nitride (BN), boron phosphide (BP),boron arsenide (BAs), gallium antimonide (GaSb), gallium arsenide(GaAs), gallium nitride (GaN), gallium phosphide (GaP), indiumantimonide (InSb), indium arsenide (InAs), indium nitride (InN), indiumphosphide (InP), aluminum gallium arsenide (AlGaAs, Al_(x)Ga_(1-x)As),indium gallium arsenide (InGaAs, In_(x)Ga_(1-x)As), indium galliumphosphide (InGaP), aluminum indium arsenide (AlInAs), aluminum indiumantimonide (AllnSb), gallium arsenide nitride (GaAsN), gallium arsenidephosphide (GaAsP), aluminum gallium nitride (AlGaN), aluminum galliumphosphide (AlGaP), indium gallium nitride (InGaN), indium arsenideantimonide (InAsSb), indium gallium antimonide (InGaSb), aluminumgallium indium phosphide (AlGaInP), aluminum gallium arsenide phosphide(AlGaAsP), indium gallium arsenide phosphide (InGaAsP), aluminum indiumarsenide phosphide (AlInAsP), aluminum gallium arsenide nitride(AlGaAsN), indium gallium arsenide nitride (InGaAsN), indium aluminumarsenide nitride (InAlAsN), gallium arsenide antimonide nitride(GaAsSbN), gallium indium nitride arsenide antimonide (GaInNAsSb),gallium indium arsenide antimonide phosphide (GaInAsSbP), andcombinations thereof.

The semiconductor material can be of any thickness that allows thedesired property or functionality of the semiconductor device, and thusany such thickness of semiconductor material is considered to be withinthe present scope. The textured region can increase the efficiency ofthe device such that, in some aspects, the semiconductor material can bethinner than has previously been possible. Decreasing the thicknessreduces the amount of semiconductor material used to make such a device.In one aspect, for example, a semiconductor material such as thesemiconductor layer has a thickness of from about 500 nm to about 50 μm.In another aspect, the semiconductor material has a thickness of lessthan or equal to about 500 μm. In yet another aspect, the semiconductormaterial has a thickness of from about 1 μm to about 10 μm. In a furtheraspect, the semiconductor material can have a thickness of from about 5μm to about 750 μm. In yet a further aspect, the semiconductor materialcan have a thickness of from about 5 μm to about 100 μm.

Additionally, various configurations of semiconductor materials arecontemplated, and any such material configuration that can beincorporated into a semiconductor device is considered to be within thepresent scope. In one aspect, for example, the semiconductor materialcan include monocrystalline materials. In another aspect, thesemiconductor material can include multicrystalline materials. In yetanother aspect, the semiconductor material can include microcrystallinematerials. It is also contemplated that the semiconductor material caninclude amorphous materials.

As has been described, the semiconductor substrate can be of any size,shape, and material capable of supporting the semiconductor layer andassociated components during manufacture and/or use. The semiconductorsubstrate can be made from various materials, including thesemiconductor materials described above, as well as non-semiconductormaterials. Non-limiting examples of such materials can include metals,polymeric materials, ceramics, glass, and the like. In some aspects, thesemiconductor substrate and the semiconductor layer have the same orsubstantially the same thermal expansion properties.

Furthermore, the semiconductor material according to aspects of thepresent disclosure can comprise multiple layers. In some aspects, layerscan vary in majority carrier polarity (i.e. donor or acceptorimpurities). The donor or acceptor impurities are typically determinedby the type of dopant/impurities introduced into the device eitherthrough a growth process, deposition process, epitaxial process, implantprocess, lasing process or other known process to those skilled in theart. In some aspects such semiconductor materials can include an n-typelayer, an intrinsic (i-type) layer, and a p-type layer, thus forming ap-i-n semiconductor material stack that creates a junction and/ordepletion region. A semiconductor material devoid of an i-type layer isalso contemplated in accordance with the present disclosure. In otheraspects the semiconductor material may include multiple junctions.Additionally, in some aspects, variations of n(−−), n(−), n(+), n(++),p(−−), p(−), p(+), or p(++) type semiconductor layers can be used. Theminus and positive signs are indicators of the relative magnitude of thedoping of the semiconductor material.

A variety of dopant materials are contemplated for both the formation ofdoped regions in the semiconductor layer and for doping of the texturedregion, and any dopant that can be used in such processes to modify amaterial is considered to be within the present scope. It should benoted that the particular dopant utilized can vary depending on thematerial being doped, as well as the intended use of the resultingmaterial.

A dopant can be either a charge donating or a charge accepting dopantspecies. More specifically, an electron donating or a hole donatingspecies can cause a region to become more positive or negative inpolarity as compared to the substrate upon which the rests. In oneaspect, for example, the doped region can be p-doped. In another aspectthe doped region can be n-doped.

In one aspect, non-limiting examples of dopant materials can include S,F, B, P, N, As, Se, Te, Ge, Ar, Ga, In, Sb, and combinations thereof. Itshould be noted that the scope of dopant materials should include, notonly the dopant materials themselves, but also materials in forms thatdeliver such dopants (i.e. dopant carriers). For example, S dopantmaterials includes not only S, but also any material capable being usedto dope S into the target region, such as, for example, H₂S, SF₆, SO₂,and the like, including combinations thereof. In one specific aspect,the dopant can be S. Sulfur can be present at an ion dosage level offrom about 5×10¹⁴ to about 3×10²⁰ ions/cm². Non-limiting examples offluorine-containing compounds can include ClF₃, PF₅, F₂ SF₆, BF₃, GeF₄,WF₆, SiF₄, HF, CF₄, CHF₃, CH₂F₂, CH₃F, C₂F₆, C₂HF₅, C₃F₈, C₄F₈, NF₃, andthe like, including combinations thereof. Non-limiting examples ofboron-containing compounds can include B(CH₃)₃, BF₃, BCl₃, BN, C₂B₁₀H₁₂,borosilica, B₂H₆, and the like, including combinations thereof.Non-limiting examples of phosphorous-containing compounds can includePF₅, PH₃, POCl₃, P₂O₅, and the like, including combinations thereof.Non-limiting examples of chlorine-containing compounds can include Cl₂,SiH₂Cl₂, HCl, SiCl₄, and the like, including combinations thereof.Dopants can also include arsenic-containing compounds such as AsH₃ andthe like, as well as antimony-containing compounds. Additionally, dopantmaterials can include mixtures or combinations across dopant groups,i.e. a sulfur-containing compound mixed with a chlorine-containingcompound. In one aspect, the dopant material can have a density that isgreater than air. In one specific aspect, the dopant material caninclude Se, H₂S, SF₆, or mixtures thereof. In yet another specificaspect, the dopant can be SF₆ and can have a predetermined concentrationrange of about 5.0×10⁻⁸ mol/cm³ to about 5.0×10⁻⁴ mol/cm³. As onenon-limiting example, SF₆ gas is a good carrier for the incorporation ofsulfur into a substrate via a laser process without significant adverseeffects on the material. Additionally, it is noted that dopants can alsobe liquid solutions of n-type or p-type dopant materials dissolved in asolution such as water, alcohol, or an acid or basic solution. Dopantscan also be solid materials applied as a powder or as a suspension driedonto the wafer.

In another aspect, the band structure optimization can be realized byforming a heterojunction along a modified semiconductor interface. Forexample, a layer of amorphous silicon can be deposited on the texturedregion interface, thus forming a heterojunction that bends the minoritycarrier band towards the desired energy direction.

1. A light trapping device, comprising: at least one light sensitivepixel having a light incident surface, a backside surface opposite thelight incident surface, and a peripheral sidewall disposed into at leasta portion of the pixel and extending at least substantially around thepixel periphery; a backside light trapping material substantiallycovering the backside surface; and a peripheral light trapping materialsubstantially covering the peripheral sidewall; wherein light contactingthe backside light trapping material or the peripheral light trappingmaterial is reflected back toward the pixel.
 2. The device of claim 1,wherein at least one of the backside light trapping material and theperipheral light trapping material includes a high refractive indexmaterial sandwiched between two low refractive index materials.
 3. Thedevice of claim 1, wherein the backside light trapping material and theperipheral light trapping material includes a high refractive indexmaterial sandwiched between two low refractive index materials.
 4. Thedevice of claim 3, wherein the two low refractive index materials have arefractive index of less than about 2.1.
 5. The device of claim 4,wherein at least one of the two low refractive index material includes amember selected from the group consisting of an oxide, a nitride,oxynitrides, a gas, at least a partial vacuum, and combinations thereof.6. The device of claim 4, wherein the at least one of the two lowrefractive index materials includes a member selected from the groupconsisting of silicon oxide, silicon nitride, silicon dioxide, andcombinations thereof.
 7. The device of claim 3, wherein the highrefractive index material includes a material having a refractive indexof greater than or equal to about 2.1.
 8. The device of claim 7, whereinthe high refractive index material includes a member selected from thegroup consisting of polycrystalline silicon, amorphous silicon, singlecrystal silicon, multicrystalline silicon, nanocrystalline silicon,germanium, and combinations thereof.
 9. The device of claim 2, whereinat least one of the two low refractive index materials is doped with adopant to create a surface field.
 10. The device of claim 9, wherein thedopant is boron or antimony.
 11. The device of claim 1, wherein at leastone of the backside light trapping material and the peripheral lighttrapping material includes a first material sandwiched between twosecond materials, wherein the first material has a higher refractiveindex as compared to the two second materials, and wherein thedifference in refractive index between the first material and the twosecond materials is at least 0.2.
 12. The device of claim 1, wherein theperipheral sidewall extends completely around the pixel periphery. 13.The device of claim 1, wherein the peripheral sidewall extends from thelight incident surface to the backside surface.
 14. The device of claim1, further comprising a frontside light trapping material at leastpartially covering the light incident surface.
 15. The device of claim14, wherein the frontside light trapping material is an antireflectivelayer coating.
 16. The device of claim 14, wherein the frontside lighttrapping material is a reflective layer having an aperture to allowentry of light into the pixel, wherein the reflective layer is operableto reflect light impinging thereupon from inside the pixel back into thepixel.
 17. The device of claim 16, further comprising a lensfunctionally coupled to the aperture and operable to focus incidentlight through the aperture and into the pixel.
 18. The device of claim16, wherein the aperture has an effective surface area of 90% of theincident light surface total surface area.
 19. The device of claim 1,wherein at least one of the backside light trapping material and theperipheral light trapping material is a metal layer.
 20. The device ofclaim 1, wherein at least one of the backside light trapping materialand the peripheral light trapping material has a sloped surface at thepixel device interface. 21-33. (canceled)